Peroxydisulfate activation by B-BC@Fe3S4 for norfloxacin degradation: Radical and non-radical pathways

In the present study, B-doped biochar loaded with Fe3S4 (B-BC@Fe3S4) was prepared and applied for peroxydisulfate (PDS) activation to remove norfloxacin (NOR). The physical-chemical properties of B-BC@Fe3S4 were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM), infrared spectrum (FTIR), Raman and X-ray photoelectron spectroscopy (XPS), respectively. Effect of different operating parameters, including PDS concentration, B-BC@Fe3S4 dosage, initial pH value, inorganic anions, humic acid (HA) and different types of water, on NOR degradation were examined systematically. Under ideal circumstances, NOR can be totally removed within 60 min with the concentration of 30 mg L−1. Quenching tests and electron paramagnetic spectrometer (EPR) analyses revealed that the dominant active species in the oxidation system were SO4·−, ·OH, ·O2− and 1O2. PDS was not only activated by Fe3S4 through electron transfer to produce radical oxidants (e.g., SO4·−, ·OH and ·O2−), but also activated by B-containing functional groups to form non-radical oxidant of 1O2. The degradation route was hypothesized combined intermediates analyzation using LC-MS detection and active sites identification using density functional theory (DFT) calculation. Results demonstrated that piperazine ring breakage and quinolone moieties transformation were two dominate pathways for NOR degradation. These results demonstrated that B-BC@Fe3S4 was efficient for PDS activation to remove antibiotics for practical application.